For Firefox users; you are already ahead of the curve by simply NOT USING Internet Explorer. For you folks still using IE, get with the program and download Firefox, Chrome or even Safari, but for Pete’s sake, dump IE. You’re making the rest of the human race look bad.
Anyway, Firefox has some really cool plugins (Adblock Plus or XMarks included) and TinEye is certainly one of them. I help my kids find cool desktop backgrounds for their computers and sometimes the pics they like are too small to make decent backgrounds. TinEye allows you to search the web for better versions of the same or similar images.
From the site:
TinEye is a reverse image search engine. The plugin adds a right-click menu item that allows you to search for an image to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution versions.